An electronic watch employs a crystal-controlled oscillator for developing a high frequency time standard, solid state logic circuits driven by the oscillator for producing timing signals, and a low power consumption solid state display responsive to the timing signals for producing time-denoting digital indicia. These components are incorporated in modules that have exposed contacts by which modular interconnections are achieved when assembled into a watch case.
In order to activate the display and render the indicia visible, and in order to set the digits of the display when the power supply is changed, the case may be provided with one or more manually operable switches. Many electronic watches utilize a push button type of switch similar to that shown in U.S. Pat. No. 3,783,607, When the exposed head of such a push button is manually depressed sufficiently far, a metal stem connected to the head and spring biased to a rear terminal position, moves forwardly into mechanical and hence electrical engagement with an exposed contact (termed a switching contact) carried by a module associated with the push button. Such engagement effects the desired switching operation by completing an electrical connection between the contact and the watch case which provides a convenient reference potential (ground) for the circuitry of the watch.
Assembly an electronic watch involves inserting the necessary modules into a case on which the required push button assemblies have been mounted. Upon final assembly, the contact of the module associated with a push button assembly should be located a predetermined distance from the forward end of the stem of the push button assembly when the stem is in its rear terminal position in order for each push button assembly to have a uniform stroke. Uniformity has not been achieved, however, in the volume production of electronic watches because of the manufacturing tolerances on electronic modules, cases and push button assemblies which are mass produced by different manufacturers. By reason of the accumulation of tolerances on particular components chosen for assembly, the stroke of a push button assembly necessary to electrically connect a contact on a module to the case may vary widely from one push button assembly to another. Furthermore, under worst-case conditions of accumulated tolerances, the available stroke of a given push button assembly may be too short to enable its stem to electrically engage its associated contact.
Much effort has been devoted to this problem, but so far as is known, no realistic solution has heretofore been found other than reducing manufacturing tolerances, a solution that drives up manufacturing costs without achieving any compensatory improvement in product performance. It is therefore an object of the present invention to provide a new and improved push button assembly for an electronic watch wherein the length of the stroke of the stem of the push button assembly necessary to achieve an electrical connection with its associated contact is fixed and independent of manufacturing tolerances on the case and on the modules.